The proposed Phase II research will develop coatings for implant devices that will greatly reduce thrombus formation upon contact with blood. The Phase I research developed procedures to immobilize hirudin onto polymers with: 1) a high retention of specific activity (one thrombin bound per two immobilized hirudin) and 2) a high loading density (sufficient hirudin was immobilized to bind and inactivate a monolayer of thrombin). Phase II will use proprietary BSI photochemistry to immobilize four classes of antithrombotic agents (hirudin, heparin, fibrinolytic enzymes, and prostaglandins) onto two implant device polymers (polyurethane and silicone rubber) and evaluate each in "side-by-side" blood compatibility assays. These agents immobilized individually and in combination will be evaluated for: 1) immobilized loading level, 2) ligand binding, 3) protease activity, 4) platelet binding and activation, and 5) thrombus formation. The assay media/systems will progress from: 1) buffers and plasma in static assays, to 2) whole blood in an in vitro recirculating loop, to 3) animal implants. The results are expected to demonstrate which agents or combinations of agents are most effective at inhibiting thrombus formation. Near the end of the project, additional devices of interest to potential Phase III partners will be coated with the most promising antithrombotic agents.